diff options
Diffstat (limited to 'include/linux/overflow.h')
| -rw-r--r-- | include/linux/overflow.h | 350 |
1 files changed, 140 insertions, 210 deletions
diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 659045046468..1d3be1a2204c 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -3,14 +3,13 @@ #define __LINUX_OVERFLOW_H #include <linux/compiler.h> +#include <linux/limits.h> +#include <linux/const.h> /* - * In the fallback code below, we need to compute the minimum and - * maximum values representable in a given type. These macros may also - * be useful elsewhere, so we provide them outside the - * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block. - * - * It would seem more obvious to do something like + * We need to compute the minimum and maximum values representable in a given + * type. These macros may also be useful elsewhere. It would seem more obvious + * to do something like: * * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0) * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0) @@ -31,7 +30,6 @@ * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html - * credit to Christian Biere. */ -#define is_signed_type(type) (((type)(-1)) < (type)1) #define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type))) #define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T))) #define type_min(T) ((T)((T)-type_max(T)-(T)1)) @@ -43,191 +41,82 @@ #define is_non_negative(a) ((a) > 0 || (a) == 0) #define is_negative(a) (!(is_non_negative(a))) -#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW -/* - * For simplicity and code hygiene, the fallback code below insists on - * a, b and *d having the same type (similar to the min() and max() - * macros), whereas gcc's type-generic overflow checkers accept - * different types. Hence we don't just make check_add_overflow an - * alias for __builtin_add_overflow, but add type checks similar to - * below. - */ -#define check_add_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - __builtin_add_overflow(__a, __b, __d); \ -}) - -#define check_sub_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - __builtin_sub_overflow(__a, __b, __d); \ -}) - -#define check_mul_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - __builtin_mul_overflow(__a, __b, __d); \ -}) - -#else - - -/* Checking for unsigned overflow is relatively easy without causing UB. */ -#define __unsigned_add_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - *__d = __a + __b; \ - *__d < __a; \ -}) -#define __unsigned_sub_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - *__d = __a - __b; \ - __a < __b; \ -}) -/* - * If one of a or b is a compile-time constant, this avoids a division. - */ -#define __unsigned_mul_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - *__d = __a * __b; \ - __builtin_constant_p(__b) ? \ - __b > 0 && __a > type_max(typeof(__a)) / __b : \ - __a > 0 && __b > type_max(typeof(__b)) / __a; \ -}) - /* - * For signed types, detecting overflow is much harder, especially if - * we want to avoid UB. But the interface of these macros is such that - * we must provide a result in *d, and in fact we must produce the - * result promised by gcc's builtins, which is simply the possibly - * wrapped-around value. Fortunately, we can just formally do the - * operations in the widest relevant unsigned type (u64) and then - * truncate the result - gcc is smart enough to generate the same code - * with and without the (u64) casts. + * Allows for effectively applying __must_check to a macro so we can have + * both the type-agnostic benefits of the macros while also being able to + * enforce that the return value is, in fact, checked. */ +static inline bool __must_check __must_check_overflow(bool overflow) +{ + return unlikely(overflow); +} -/* - * Adding two signed integers can overflow only if they have the same - * sign, and overflow has happened iff the result has the opposite - * sign. +/** + * check_add_overflow() - Calculate addition with overflow checking + * @a: first addend + * @b: second addend + * @d: pointer to store sum + * + * Returns 0 on success. + * + * *@d holds the results of the attempted addition, but is not considered + * "safe for use" on a non-zero return value, which indicates that the + * sum has overflowed or been truncated. */ -#define __signed_add_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - *__d = (u64)__a + (u64)__b; \ - (((~(__a ^ __b)) & (*__d ^ __a)) \ - & type_min(typeof(__a))) != 0; \ -}) +#define check_add_overflow(a, b, d) \ + __must_check_overflow(__builtin_add_overflow(a, b, d)) -/* - * Subtraction is similar, except that overflow can now happen only - * when the signs are opposite. In this case, overflow has happened if - * the result has the opposite sign of a. +/** + * check_sub_overflow() - Calculate subtraction with overflow checking + * @a: minuend; value to subtract from + * @b: subtrahend; value to subtract from @a + * @d: pointer to store difference + * + * Returns 0 on success. + * + * *@d holds the results of the attempted subtraction, but is not considered + * "safe for use" on a non-zero return value, which indicates that the + * difference has underflowed or been truncated. */ -#define __signed_sub_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - *__d = (u64)__a - (u64)__b; \ - ((((__a ^ __b)) & (*__d ^ __a)) \ - & type_min(typeof(__a))) != 0; \ -}) +#define check_sub_overflow(a, b, d) \ + __must_check_overflow(__builtin_sub_overflow(a, b, d)) -/* - * Signed multiplication is rather hard. gcc always follows C99, so - * division is truncated towards 0. This means that we can write the - * overflow check like this: +/** + * check_mul_overflow() - Calculate multiplication with overflow checking + * @a: first factor + * @b: second factor + * @d: pointer to store product * - * (a > 0 && (b > MAX/a || b < MIN/a)) || - * (a < -1 && (b > MIN/a || b < MAX/a) || - * (a == -1 && b == MIN) + * Returns 0 on success. * - * The redundant casts of -1 are to silence an annoying -Wtype-limits - * (included in -Wextra) warning: When the type is u8 or u16, the - * __b_c_e in check_mul_overflow obviously selects - * __unsigned_mul_overflow, but unfortunately gcc still parses this - * code and warns about the limited range of __b. + * *@d holds the results of the attempted multiplication, but is not + * considered "safe for use" on a non-zero return value, which indicates + * that the product has overflowed or been truncated. */ +#define check_mul_overflow(a, b, d) \ + __must_check_overflow(__builtin_mul_overflow(a, b, d)) -#define __signed_mul_overflow(a, b, d) ({ \ - typeof(a) __a = (a); \ - typeof(b) __b = (b); \ - typeof(d) __d = (d); \ - typeof(a) __tmax = type_max(typeof(a)); \ - typeof(a) __tmin = type_min(typeof(a)); \ - (void) (&__a == &__b); \ - (void) (&__a == __d); \ - *__d = (u64)__a * (u64)__b; \ - (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \ - (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \ - (__b == (typeof(__b))-1 && __a == __tmin); \ -}) - - -#define check_add_overflow(a, b, d) \ - __builtin_choose_expr(is_signed_type(typeof(a)), \ - __signed_add_overflow(a, b, d), \ - __unsigned_add_overflow(a, b, d)) - -#define check_sub_overflow(a, b, d) \ - __builtin_choose_expr(is_signed_type(typeof(a)), \ - __signed_sub_overflow(a, b, d), \ - __unsigned_sub_overflow(a, b, d)) - -#define check_mul_overflow(a, b, d) \ - __builtin_choose_expr(is_signed_type(typeof(a)), \ - __signed_mul_overflow(a, b, d), \ - __unsigned_mul_overflow(a, b, d)) - - -#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */ - -/** check_shl_overflow() - Calculate a left-shifted value and check overflow - * +/** + * check_shl_overflow() - Calculate a left-shifted value and check overflow * @a: Value to be shifted * @s: How many bits left to shift * @d: Pointer to where to store the result * * Computes *@d = (@a << @s) * - * Returns true if '*d' cannot hold the result or when 'a << s' doesn't + * Returns true if '*@d' cannot hold the result or when '@a << @s' doesn't * make sense. Example conditions: - * - 'a << s' causes bits to be lost when stored in *d. - * - 's' is garbage (e.g. negative) or so large that the result of - * 'a << s' is guaranteed to be 0. - * - 'a' is negative. - * - 'a << s' sets the sign bit, if any, in '*d'. * - * '*d' will hold the results of the attempted shift, but is not - * considered "safe for use" if false is returned. + * - '@a << @s' causes bits to be lost when stored in *@d. + * - '@s' is garbage (e.g. negative) or so large that the result of + * '@a << @s' is guaranteed to be 0. + * - '@a' is negative. + * - '@a << @s' sets the sign bit, if any, in '*@d'. + * + * '*@d' will hold the results of the attempted shift, but is not + * considered "safe for use" if true is returned. */ -#define check_shl_overflow(a, s, d) ({ \ +#define check_shl_overflow(a, s, d) __must_check_overflow(({ \ typeof(a) _a = a; \ typeof(s) _s = s; \ typeof(d) _d = d; \ @@ -237,83 +126,124 @@ *_d = (_a_full << _to_shift); \ (_to_shift != _s || is_negative(*_d) || is_negative(_a) || \ (*_d >> _to_shift) != _a); \ -}) +})) /** - * array_size() - Calculate size of 2-dimensional array. - * - * @a: dimension one - * @b: dimension two + * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX + * @factor1: first factor + * @factor2: second factor * - * Calculates size of 2-dimensional array: @a * @b. - * - * Returns: number of bytes needed to represent the array or SIZE_MAX on - * overflow. + * Returns: calculate @factor1 * @factor2, both promoted to size_t, + * with any overflow causing the return value to be SIZE_MAX. The + * lvalue must be size_t to avoid implicit type conversion. */ -static inline __must_check size_t array_size(size_t a, size_t b) +static inline size_t __must_check size_mul(size_t factor1, size_t factor2) { size_t bytes; - if (check_mul_overflow(a, b, &bytes)) + if (check_mul_overflow(factor1, factor2, &bytes)) return SIZE_MAX; return bytes; } /** - * array3_size() - Calculate size of 3-dimensional array. + * size_add() - Calculate size_t addition with saturation at SIZE_MAX + * @addend1: first addend + * @addend2: second addend * - * @a: dimension one - * @b: dimension two - * @c: dimension three - * - * Calculates size of 3-dimensional array: @a * @b * @c. - * - * Returns: number of bytes needed to represent the array or SIZE_MAX on - * overflow. + * Returns: calculate @addend1 + @addend2, both promoted to size_t, + * with any overflow causing the return value to be SIZE_MAX. The + * lvalue must be size_t to avoid implicit type conversion. */ -static inline __must_check size_t array3_size(size_t a, size_t b, size_t c) +static inline size_t __must_check size_add(size_t addend1, size_t addend2) { size_t bytes; - if (check_mul_overflow(a, b, &bytes)) - return SIZE_MAX; - if (check_mul_overflow(bytes, c, &bytes)) + if (check_add_overflow(addend1, addend2, &bytes)) return SIZE_MAX; return bytes; } -/* - * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for - * struct_size() below. +/** + * size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX + * @minuend: value to subtract from + * @subtrahend: value to subtract from @minuend + * + * Returns: calculate @minuend - @subtrahend, both promoted to size_t, + * with any overflow causing the return value to be SIZE_MAX. For + * composition with the size_add() and size_mul() helpers, neither + * argument may be SIZE_MAX (or the result with be forced to SIZE_MAX). + * The lvalue must be size_t to avoid implicit type conversion. */ -static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c) +static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) { size_t bytes; - if (check_mul_overflow(a, b, &bytes)) - return SIZE_MAX; - if (check_add_overflow(bytes, c, &bytes)) + if (minuend == SIZE_MAX || subtrahend == SIZE_MAX || + check_sub_overflow(minuend, subtrahend, &bytes)) return SIZE_MAX; return bytes; } /** - * struct_size() - Calculate size of structure with trailing array. + * array_size() - Calculate size of 2-dimensional array. + * @a: dimension one + * @b: dimension two + * + * Calculates size of 2-dimensional array: @a * @b. + * + * Returns: number of bytes needed to represent the array or SIZE_MAX on + * overflow. + */ +#define array_size(a, b) size_mul(a, b) + +/** + * array3_size() - Calculate size of 3-dimensional array. + * @a: dimension one + * @b: dimension two + * @c: dimension three + * + * Calculates size of 3-dimensional array: @a * @b * @c. + * + * Returns: number of bytes needed to represent the array or SIZE_MAX on + * overflow. + */ +#define array3_size(a, b, c) size_mul(size_mul(a, b), c) + +/** + * flex_array_size() - Calculate size of a flexible array member + * within an enclosing structure. + * @p: Pointer to the structure. + * @member: Name of the flexible array member. + * @count: Number of elements in the array. + * + * Calculates size of a flexible array of @count number of @member + * elements, at the end of structure @p. + * + * Return: number of bytes needed or SIZE_MAX on overflow. + */ +#define flex_array_size(p, member, count) \ + __builtin_choose_expr(__is_constexpr(count), \ + (count) * sizeof(*(p)->member) + __must_be_array((p)->member), \ + size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member))) + +/** + * struct_size() - Calculate size of structure with trailing flexible array. * @p: Pointer to the structure. * @member: Name of the array member. - * @n: Number of elements in the array. + * @count: Number of elements in the array. * * Calculates size of memory needed for structure @p followed by an - * array of @n @member elements. + * array of @count number of @member elements. * * Return: number of bytes needed or SIZE_MAX on overflow. */ -#define struct_size(p, member, n) \ - __ab_c_size(n, \ - sizeof(*(p)->member) + __must_be_array((p)->member),\ - sizeof(*(p))) +#define struct_size(p, member, count) \ + __builtin_choose_expr(__is_constexpr(count), \ + sizeof(*(p)) + flex_array_size(p, member, count), \ + size_add(sizeof(*(p)), flex_array_size(p, member, count))) #endif /* __LINUX_OVERFLOW_H */ |